Plenarvorträge - DPG-Tagungen
Plenarvorträge - DPG-Tagungen
Plenarvorträge - DPG-Tagungen
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Magnetismus Donnerstag<br />
resonante Mode auf, bei der die Position des Vortex auf einer Kreisbahn<br />
um den Mittelpunkt der Kreisscheibe mit der Frequenz des angelegten<br />
Felds rotiert [2]. Bei höherer Frequenz von ca. 5 GHz enteht eine resonante<br />
Mode anderen Typs, bei der stehende Wellen innerhalb der Kreisscheibe<br />
angeregt werden. [1] A. Wachowiak et al., Science 298, (5593)<br />
577 (2002) [2] Guslienko et al., J. Appl. Phys. 91 (10) 8037 (2002)<br />
MA 28.5 Do 16:15 H23<br />
Spin Dynamics in Permalloy Disks with Vortex Structure<br />
— •Matthias Buess 1,2 , Rainer Höllinger 1 , Thomas<br />
Haug 1 , Korbinian Perzlmaier 1 , Michael R. Scheinfein<br />
3 , Danilo Pescia 2 , and Christian H. Back 1 — 1 Institut<br />
fürExperimentelle und Angewandte Physik, Universität Regensburg,<br />
Universitätsstrasse 31, 93040 Regensburg, Germany — 2 Laboratorium<br />
für Festkörperphysik,Eidgenössische Technische Hochschule Zürich,<br />
CH-8093Zürich,Switzerland — 3 Simon Fraser University, 8888 University<br />
Drive, Burnaby BC U5A 156, Canada<br />
Micron sized ferromagnetic permalloy disks exhibiting a ferromagnetic<br />
vortex structure are excited by a magnetic field pulse. The fast rise time<br />
pulse field is generated by an optically triggered electrical pulse in a lithographically<br />
fabricated microcoil. The excitation is imaged using time resolved<br />
magneto-optic polar Kerr microscopy - a stroboscopic experiment.<br />
We present the spatially resolved magnetic maps at different delay times,<br />
stitched together to form a magnetic movie. The dynamical excitations<br />
are composed of symmetric and non-sysmmetric parts which can not be<br />
separated at first glance. However, in the Fourier transformation of the<br />
magnetic movie we identify several modes which can be accounted for<br />
in a simple model based on purely dipolar interactions. The model is<br />
supported by micromagnetic simulations and shows good quantitative<br />
agreement in the resonance frequencies for different modes and sample<br />
dimensions.<br />
MA 28.6 Do 16:30 H23<br />
NANOSECOND TIME-SCALE SWITCHING OF THIN FILM<br />
PERMALLOY ELEMENTS — •Dmitry Chumakov, Rudolf<br />
Schäfer, Jeffrey McCord, and Ludwig Schultz — IFW-Dresden,<br />
Helmholtzstr. 20, D-01069 Dresden, Germany<br />
We have studied the dynamic magnetization switching behaviour of<br />
thin film Permalloy elements by gated ICCD camera-based time-resolved<br />
wide-field Kerr microscopy. The structures were subject to pulsed magnetic<br />
fields of different strengths from 1600 A/m to 5200 A/m. Their<br />
reversal was observed with 250 ps time-resolution. By interpreting the<br />
experimental results we point out the peculiarities of the nanosecond<br />
timescale switching. Like in the quasistatic case, the dynamic remagnetization<br />
process is dominated by the generation of concertina-like domain<br />
patterns. Whereas such ”blocked” domains decay irreversibly in several<br />
steps during quasistatic switching, the blocking is resolved by continuous<br />
rotation in a locally inhomogeneous way for dynamic switching. This<br />
process lasts several nanoseconds and leads to significant delays in element<br />
switching. The influence of magnetic field amplitude, rise-time,<br />
and element shape on the switching behaviour will be shown at various<br />
examples.<br />
MA 28.7 Do 16:45 H23<br />
Magnetization Dynamics of Micron Sized Permalloy Squares —<br />
•Korbinian Perzlmaier, Christian Back, Matthias Buess, and<br />
Rainer Höllinger — Institut für Experimentelle und Angewandte<br />
Physik, Universität Regensburg, Universitätsstrasse 31, 93040 Regensburg<br />
We investigate the dynamic response of the magnetization in micron<br />
sized Permalloy squares by measuring the polar Kerr component in a<br />
time resolved Kerr-microscope. The sample is excited with a fast rise<br />
time magnetic field pulse (typically pulse fields are smaller than 100 Oe)<br />
applied perpendicular to the sample plane. Magnetic movies are recorded<br />
with a frame rate of 10 ps. From the Fourier transform of the data we<br />
obtain information about the modal frequencies.<br />
Numerical methods based on the LLG equation are commonly used<br />
to simulate the dynamic response of magnetic elements. We extract the<br />
modal structure from simulated movies of squares in the size range between<br />
300 nm and 4 micron. The results are compared to our experiments.<br />
MA 28.8 Do 17:00 H23<br />
Investigation of magnetization dynamics of microstructured<br />
magnetic thin films by means of Time-Resolved Photoemission<br />
Electron Microscopy. — •A. Krasyuk 1 , A. Oelsner 1 , S.A.<br />
Nepijko 1 , D. Neeb 1 , A. Kuksov 2 , C.M. Schneider 2 und G.<br />
Schönhense 1 — 1 Johannes Gutenberg-Universität Mainz, Institut<br />
für Physik, Staudinger Weg 7, 55099 Mainz, Germany — 2 Institut für<br />
Festkörperforschung, Forschungszentrum Jülich, 52425 Jülich, Germany<br />
The magnetisation reversal dynamics of the lithographically prepared<br />
Permalloy particles with different forms and thickness ranging from<br />
10nm up to 40nm was observed exploiting the Magnetic X-Ray Circular<br />
Dichroism (MXCD) contrast at the Ni L3 X-ray absorption edges in subns<br />
range by means Time-Resolved Photoemission Electron Microscope.<br />
The experiment has been performed in single-bunch mode at the BESSY<br />
II (Berlin) and 16-bunch mode at the ESRF (Grenoble). [1] A. Krasyuk,<br />
A. Oelsner, S.A. Nepijko, A. Kuksov, C.M. Schneider, G. Schönhense.,<br />
Appl.Phys.A, 2003, 76, No.6, 863-868. [2] A. Oelsner, A. Krasyuk, D.<br />
Neeb, S.A. Nepijko, A. Kuksov, C.M. Schneider, G. Schönhense., J. Electr.<br />
Spectr. Rel. Phenom, accepted<br />
MA 28.9 Do 17:15 H23<br />
Damping in thin NiFe films — •Hans Nembach, Markus C. Weber,<br />
Jürgen Fassbender, and Burkard Hillebrands — Fachbereich<br />
Physik und Forschungsschwerpunkt MINAS, Technische Universität<br />
Kaiserslautern, Erwin-Schrödinger-Str. 56, 67663 Kaiserslautern<br />
We investigated the damping and spin wave creation in thin NiFe films<br />
with time-resolved magneto-optic Kerr effect magnetometry for small and<br />
large angle excitations. To gain further insight in the underlying damping<br />
process we employ a special measurement procedure, which allows<br />
us to determine all three magnetization vector components and therefore<br />
the length of the magnetization vector. A reduction of the magnitude<br />
of the magnetization vector indicates the creation of spin waves. These<br />
spin waves can be created directly by the stripline or by multi-magnon<br />
processes.<br />
The experimentally determined magnetization trajectory is compared<br />
with numerical simulations based on the Landau-Lifshitz equation, and<br />
the damping constant is extracted from these simulations<br />
MA 28.10 Do 17:30 H23<br />
Dependence of magnetization reversal dynamics on magnetic<br />
anisotropy and interlayer coupling — •K. Fukumoto 1 , W.<br />
Kuch 1 , J. Vogel 2 , J. Camarero 3 , S. Pizzini 2 , Y. Pennec 2 ,<br />
F. Offi 1 , M. Bonfim 4 , A. Fontaine 2 , and J. Kirschner 1 —<br />
1 Max-Planck-Institut für Mikrostrukturphysik, Weinberg 2, D-06120<br />
Halle, Germany — 2 Laboratoire Louis Néel, CNRS, 25 Avenue des<br />
Martyrs, B. P. 166, F-38042 Grenoble Cedex 9, France — 3 Dpto. Física<br />
de la Materia Condensada, Universidad Autónoma de Madrid, E-28049<br />
Madrid, Spain — 4 Departamento de Engenharia Elètrica, Universidade<br />
do Paraná, CEP 81531-990, Curitiba, Brazil<br />
Time- and element-resolved magnetic domain imaging measurements<br />
were performed using x-ray magnetic circular dichroism photoelectron<br />
emission microscopy (XMCD-PEEM). Two types of spin-valve-like samples<br />
(Fe20Ni80/Cu/Co) were used in this study, one with and one without<br />
magnetic anisotropy in the film plane. Magnetization reversal during<br />
nanosecond-short magnetic field pulses was investigated by a pumpprobe<br />
technique. Domain wall motion induced by the field pulses (pump)<br />
was imaged using photon pulses from single bunch operation of BESSY<br />
(probe). Magnetization reversal and domain structure of the permalloy<br />
layer in the sample showing no anisotropy in the plane are strongly influenced<br />
by local pinning. In the sample with in-plane anisotropy, domain<br />
patterns during the reversal of the permalloy layer are less reproducible,<br />
and more influenced by the local coupling with the Co layer. Reversal<br />
mechanism, speed of domain wall motion, and the effect of magnetic<br />
interlayer coupling were also studied using single-pulse measurements.<br />
MA 28.11 Do 17:45 H23<br />
All optical probe of coherent spin waves in exchange bias<br />
systems — •B. Beschoten 1 , A. Tillmanns 1 , S. Oertker 1 , G.<br />
Güntherodt 1 , I.K. Schuller 2 , C. Leighton 3 , and J. Nogués 4<br />
— 1 2. Physikalisches Institut, RWTH Aachen, 52056 Aachen —<br />
2 Department of Physics, UC San Diego — 3 Department of Chemical<br />
Engineering and Materials Science, University of Minnesota —<br />
4 Departament de Fisica, Universitat Autònoma de Barcelona<br />
Time-resolved Kerr rotation is used to generate and to probe coherent<br />
spin waves in exchange biased ferro-/antiferromagnetic bilayer films of